[CF-metadata] What do models assume for the shape of the Earth?

Bryan Lawrence b.n.lawrence at rl.ac.uk
Thu Apr 7 01:20:49 MDT 2005

On Wednesday 06 April 2005 20:19, Jonathan Gregory wrote:
> The data provider probably doesn't care very much. This information is not
> seen as critical for interpretation or even formulation of the model. Hence
> you can probably legitimately serve it using any reasonable assumption.

I would go even further than this. While it is possible that the coordinate 
transformation error becomes more significant at very high resolution global 
models and mesoscale model scales, the actual significance of the model 
results at those scales is poor (typically, for a grid point model, one 
should be looking at an effective resolution about four times the grid 
resolution).  What that means is the error in the grid projection 
transformation (if there is one) is vastly smaller than the effective grid 
registration (ie. how accurately the model coordinates reflect the real 
world). This is probably true even in a data assimilation model, where the 
model knows a bit more about the real world ... 

Nowcasting models at the very finest scales may be a different story, but in 
that case the grid formulation should probably be rather different than a 
global spherical formulation ...  ("should" I say, don't know that they 
are :-)
I don't think that CF can cope with everything ...


Bryan Lawrence
Head, NCAS/British Atmospheric Data Centre
Director, CCLRC/Environmental Data Archival and Associated Research
badc.nerc.ac.uk, home.badc.rl.ac.uk/lawrence, +44 1235 445012
(CCLRC, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX)

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